[Illustration: OLIVE MOUNT CUTTING. [By Percival Skelton.]] The Olive Mount cutting was the first extensive stone cutting executed on any railway, and to this day it is one of the most formidable. It is about two miles long, and in some parts more than a hundred feet deep. It is a narrow ravine or defile cut out of the solid rock, and not less than four hundred and eighty thousand cubic yards of stone were removed from it. Mr. Vignolles, afterward describing it, said it looked as if it had been dug out by giants. [Illustration: SANKEY VIADUCT. [By Percival Skelton.]] The crossing of so many roads and streams involved the necessity for constructing an unusual number of bridges. There were not fewer than sixty-three, under or over the railway, on the thirty miles between Liverpool and Manchester. Up to this time bridges had been applied generally to high roads, where inclined approaches were of comparatively small importance, and in determining the rise of his arch the engineer selected any headway he thought proper. Every consideration was indeed made subsidiary to constructing the bridge itself, and the completion of one large structure of this sort was regarded as an epoch in engineering history. Yet here, in the course of a few years, no fewer than sixty-three bridges were constructed on one line of railway! Mr. Stephenson early found that the ordinary arch was inapplicable in certain cases, where the headway was limited, and yet the level of the railway must be preserved. In such cases he employed simple cast-iron beams, by which he safely bridged gaps of moderate width, economizing headway, and introducing the use of a new material of the greatest possible value to the engineer. The bridges of masonry upon the line were of many kinds; several of them were skew bridges, while others, such as those at Newton and over the Irwell at Manchester, were straight and of considerable dimensions. But the principal piece of masonry on the line was the Sankey viaduct. This fine work is principally of brick, with stone facings. It consists of nine arches of fifty feet span each. The massive piers are supported on two hundred piles driven deep into the soil; and they rise to a great height--the coping of the parapet being seventy feet above the level of the valley, in which flow the Sankey brook and Canal. Its total cost was about £45,000.